Glucose belongs to a class of molecules known as carbohydrates. It is a monosaccharide sugar that serves as a source of energy for living things. Its molecular formula is C6H12O6.
Linked, linear chains of glucose molecules make up cellulose. The carbohydrate cellulose is the most abundant organic compound in the biosphere. Most mammals, with the exception of ruminants, are unable to digest cellulose.
Carbohydrates are one of four major classes of molecules, in addition to proteins, lipids and nucleic acids. They are comprised of sugars and exist in various sizes. Smaller molecules may have prefixes of "mono-," "di-" and "tri-," while larger ones are termed polysaccharides.